The present invention relates to a ducted gas turbine engine and includes a nacelle assembly which is detachably connected to a ducted gas turbine engine.
Ducted gas turbine engines usually comprise a core engine which drives a propulsive fan assembly. The fan assembly comprises a number of radially extending aerofoil blades mounted on a common hub and enclosed within a generally cylindrical casing assembly. The fan assembly and casing assembly are encircled by a generally annular nacelle assembly which forms the air intake of the engine and is aerodynamically shaped. The nacelle may extend both forward and rearward, relative to the direction of airflow, of the fan assembly.
There is a remote possibility with such engines that part or all of one or more of the fan blades could become detached from the remainder of the fan assembly. The occurrence of a part or all of one or more of the fan blades becoming detached from the fan assembly and impacting the casing assembly is hereinafter termed a FBO (fan blade off) event. The casing assembly surrounding the fan assembly is specifically designed to contain the detached blade or blade portion. However, it is important that the nacelle is not damaged during the FBO event as the casing assembly is subject to distortion. It is also important to remove the possibility of further damage to the nacelle, after the FBO event, resulting from vibrations during run down and subsequent windmilling due to the fan assembly being out of balance. Run down being hereinafter defined as the deceleration of axial rotational speed of the engine from the rotational speed at which a fan blade or part of a fan blade has been released and caused safety systems to shut down the engine. Windmilling being hereinafter defined as the axial rotation of the fan assembly arising from air ingressing the engine due to the forward speed of the aircraft after engine shut down.
Typically the nacelle assembly may be attached to a component of the engine and/or an engine support pylon assembly with the necessary access to the engine and engine core mounted accessories usually made by either opening fan cowl doors located in the body of the nacelle as described in WO93/02920 or by the nacelle assembly comprising two part-circular portions acting in a clam-shell like manner as described in U.S. Pat. No. 5,205,513. Furthermore, the nacelle assembly is commonly attached to the fan casing as described in U.S. Pat. No. 4,044,973, with such attachments being required to be particularly robust to maintain attachment after a FBO event. The nacelle designs, in particular the attachment means to the engine and/or pylon, of the prior art herein cited lend themselves to complex and heavy, thus expensive, assemblies. The nacelle assemblies also appear to be prone to damage during a FBO event and subsequent vibrational damage caused by windmilling of the out of balance fan assembly during fly home.
It is an object of the present invention to provide a lightweight and low cost nacelle assembly, attached to the engine in such a way as to be releasably detachable therefrom during a FBO event and thereby isolating the nacelle assembly from potentially destructive fan assembly vibrations.
According to the present invention there is provided a nacelle assembly adapted for mounting on a ducted fan gas turbine engine comprising a generally annular body having an air inlet and an air outlet, the generally annular body encircling a region of the engine when working in operative association with the engine and has a first attachment means to a rigid member and a second attachment means to a casing assembly on the engine wherein the second attachment means is frangible.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the casing assembly comprises a containment casing and surrounds a fan assembly.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the second attachment means provides support in the radial direction.
Preferably the nacelle assembly is adapted for mounting on a gas turbine wherein the second attachment means detaches the nacelle assembly from the casing assembly during a FBO event.
Preferably a nacelle assembly adapted for mounting on a gas turbine wherein the rigid member is a component of the engine. Alternatively the nacelle assembly is adapted for mounting on a gas turbine engine wherein the rigid member is a component of a pylon structure or an aircraft structure.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the first attachment means provides support for the nacelle in the radial, axial and circumferential directions.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the first attachment means is a releasable attachment.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the annular body comprises a radially outer facing and a radially inner facing defining a space therebetween.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the annular body comprises the outer facing and inner facing joining and extending rearward of the space to form a single skin. Alternatively the nacelle assembly is adapted for mounting on a gas turbine engine wherein the outer facing and inner facing are constructed from sandwich constructions.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the space contains a lightweight core, the lightweight core attached to both the outer facing and the inner facing. Alternatively the nacelle assembly is adapted for mounting on a gas turbine engine wherein the space contains a connector, the connector attached to both the outer facing and the inner facing.
Preferably the nacelle assembly is adapted for mounting on a gas turbine engine wherein the connector extends substantially in the axial direction. Alternatively the nacelle assembly is adapted for mounting on a gas turbine engine wherein the connector extends substantially in the circumferential direction.
Preferably the nacelle assembly is adapted for mounting on a gas turbine wherein the annular body includes an access panel. Alternatively the nacelle assembly is adapted for mounting on a gas turbine engine wherein an engine accessory is operationally located within the space in the annular body.
Preferably a method for assembling a nacelle assembly with an engine comprises the steps aligning the nacelle assembly and the engine substantially parallel to the engine rotation axis, translating the nacelle assembly along the axis to engage the first and second attachments, and securing the first attachment.
Preferably a method for removing a nacelle assembly from an engine comprises the steps releasing the first attachment, translating the nacelle assembly substantially parallel to the axis of the engine.